Memoirs of Benjamin Franklin; Written by Himself. [Vol. 2 of 2]
With his Most Interesting Essays, Letters, and Miscellaneous Writings; Familiar, Moral, Political, Economical, and Philosophical, Selected with Care from All His Published Productions, and Comprising Whatever Is Most Entertaining and Valuable to the General Reader

By Benjamin Franklin

Page 210

part ofa summer's day, or, it may be, for several days successively, till it isviolently heated, together with the lower region of air in contact withit, so that the said lower air becomes specifically lighter than thesuperincumbent higher region of the atmosphere in which the cloudscommonly float: let us suppose, also, that the air surrounding thistract has not been so much heated during those days, and, therefore,remains heavier. The consequence of this should be, as I conceive, thatthe heated lighter air, being pressed on all sides, must ascend, and theheavier descend; and as this rising cannot be in all parts, or the wholearea of the tract at once, for that would leave too extensive a vacuum,the rising will begin precisely in that column that happens to be thelightest or most rarefied; and the warm air will flow horizontally fromall points to this column, where the several currents meeting, andjoining to rise, a whirl is naturally formed, in the same manner as awhirl is formed in the tub of water, by the descending fluid flowingfrom all sides of the tub to the hole in the centre.

And as the several currents arrive at this central rising column with aconsiderable degree of horizontal motion, they cannot suddenly change itto a vertical motion; therefore, as they gradually, in approaching thewhirl, decline from right curved or circular lines, so, having joinedthe whirl, they _ascend_ by a spiral motion, in the same manner as thewater _descends_ spirally through the hole in the tub before mentioned.

Lastly, as the lower air, and nearest the surface, is most rarefied bythe heat of the sun, that air is most acted on by the pressure of thesurrounding cold and heavy air, which is to take its place;consequently, its motion towards the whirl is swiftest, and so the forceof the lower part of the whirl or trump strongest, and the centrifugalforce of its particles greatest; and hence the vacuum round the axis ofthe whirl should be greatest near the earth or sea, and be graduallydiminished as it approaches the region of the clouds, till it ends in apoint, as at P, _Fig. 2. in the plate_, forming a long and sharp cone.

In figure 1, which is a plan or groundplat of a whirlwind, the circle Vrepresents the central vacuum.

Between _a a a a_ and _b b b b_ I suppose a body of air, condensedstrongly by the pressure of the currents moving

Text Comparison with The Complete Works in Philosophy, Politics and Morals of the late Dr. Benjamin Franklin, Vol. 2 [of 3]

You may possibly remember, that in or about the year 1758, you made
for me a set of artificial magnets, six in number, each five and
a half inches long, half an inch broad, and one eighth of an inch
thick.

Accordingly, about the middle of October last, I went with
some friends to Portsmouth; and a day of wind happening, which made
a lee-shore between Haslar-hospital and the point near Jillkecker,
we went from the Centaur with the long-boat and barge towards that
shore.

But an old workman observing it advised me
not to do so, telling me I might lose the use of my hands by it, as
two of our companions had nearly done, one of whom, that used to earn
his guinea a week, could not then make more than ten shillings, and
the other, who had the dangles, but seven and sixpence.

By a push with your tongs or poker, you turn it on
its pin till it faces the back of the chimney, then turn it over on
its axis gently till it again faces the room, whereby all the fresh
coals will be found under the live coals, and the greater part of the
smoke arising from the fresh coals will in its passage through the
live ones be heated so as to be converted into flame: whence you have
much more heat from them, and your red coals are longer preserved
from consuming.

I cannot but applaud your zeal for preserving the purity of our
language both in its expression and pronunciation, and in correcting
the popular errors several of our states are continually falling
into with respect to both.